1. Field of the Invention
The invention relates to a flexible bag with an incorporated opening line, a method for manufacturing such a bag, and a machine for manufacturing such a bag.
2. Background Art
The term "flexible bag" applies to any container made up of at least two walls consisting of sheets made of one or more materials flexible enough to be deformed without suffering damage under normal conditions of use.
But while being flexible, it must be possible for the user to easily cut or tear the walls so as to gain access to the product contained within without diminishing the bag's resistance.
For example, the walls can be made of a sheet of paper, a sheet of plastic material or a sheet of metal such as aluminum. They are often made out of a complex multilayered film.
Flexible bags are known of whose walls are located opposite to one another. They comprise a margin for rigidly joining the two walls together. The margin is disposed so as to delimit, on the one hand, the outer periphery of the bag, and, on the other hand, the outer contour of a central volume.
This central volume is intended to contain a product which can be liquid, pasty or pulverulent, for example. This product can consist of a fluid for nutritive, cosmetic, medical or household use.
Since this volume is surrounded, usually in an airtight manner, by the joining margin, an opening has to be formed in the walls of the bag to allow the product to be poured out.
Such an opening can be produced using a cutting tool such as a pair of scissors.
Another well known method involves providing, on the joining margin, a line of weakest resistance intended to allow the bag to be opened without using cutting tools, by tearing away or ripping the walls. A first end of the line of weakest resistance is generally located on the outer periphery of the bag.
But these bags display a number of disadvantages.
With certain materials which the walls are made of, it is not always possible to obtain a correct opening of the bag by tearing along the line of weakest resistance. This, for example, is the case with walls which comprise a layer of a material with a high tear strength, PET for example, or which is highly elastic, PE or PP for example.
On the other hand, if at least one wall comprises a layer of a material able to withstand significant elastic deformations without tearing, the opening obtained is not always well defined, and it is therefore not possible to pour out the product in a clean manner or to dose it precisely.
The tear often deviates from the direction along which one wishes it to be performed. This can result in parts of the walls being ripped without the bag being opened. The tear may also deviate towards the volume's interior, creating a breach such that the product has a tendency to leak out of the bag.
The arrangement and the limited dimensions of the known lines of weakest resistance make them difficult to locate and the grip provided is insufficient to allow for easy tearing.